Wire bonding is a method of making interconnections between a micro device and the outside world as part of semiconductor device fabrication. Wire bonding is used to electrically connect a microchip to its substrate or package. This procedure requires a metal pad on the microchip. Wire bonding is generally considered the most cost-effective and flexible interconnect technology, and is used to assemble the vast majority of semiconductor packages. In general, a gold wire is attached at both ends to a metallic layer, using some combination of heat, pressure, and ultrasonic energy to make a weld. Prior art FIG. 1a is a schematic illustration of wire bonding showing wire 105 having a standard ball-bond 110 bonded to a metal pad 120 mounted on a Single Crystal Silicon (SCS) wafer 130.
MicroElectroMechanical Systems (MEMS) and micro devices are often fabricated using passivation layers. Passivation is the process of oxidation/nitridization of a material. The passivation layers are mostly used as hard masks and electric isolation. The process of passivation requires a high temperature, of up to 1200° C.
Due to the presence of metal layers which are used as conductors and bonding pads, the process temperature is limited to 400° C. This prevents any passivation processes where metal layers exist. In micro devices the conductors may be replaced by highly doped silicon, but there is no alternative for the bonding pads, because wire bonding cannot be performed on straight smooth silicon layers.
Thus, it would be desirable to provide an alternative method that does not require bonding pads, and is not performed on straight smooth silicon layers.